Body Mass Index Considerations

The Body Mass Index, or BMI, has become the standard by which obesity and overweight is judged. Diets and exercise websites of all kinds use a BMI calculator to help their visitors understand if they have a problem with their weight. Even the FDA and bariatric surgeons use the BMI calculation as an estimation of a person’s surgical eligibility. It is important to remember however, that the BMI number is just a guide and it should not be taken as the final say on whether a person is suitable for weight loss surgery. In fact, the preoperative process to qualify someone for weight loss surgery is much deeper than just entering weight and height into a calculator.

Preoperative testing includes a general health evaluation as well as lung, kidney and heart function testing. These tests seek to determine if the patient’s surgical risk is greater than the benefit that they would receive by having surgery. After all, our primary goal is to ensure patient safety, both during and after their weight loss procedure. The BMI therefore has to be taken with a grain of salt:

  • Firstly, it does not take into account gender differences. Men tend to have larger frames. While a man and woman may be the same height and weight, their eligibility for weight loss surgery may be different.
  • To the point above, the BMI does not take into account a person’s body frame which can vary drastically. Musculature too can change a person’s reading. Remember, muscle is heavier than fat and a very muscular person may show as obese.
  • Similarly the Body Mass Index number does not account for age. As we age our muscles tend to degrade and therefore an older person’s weight may suggest the greater risk of obesity versus a younger person with a similar profile.

By not taking these issues into account, the Body Mass Index becomes somewhat unreliable as definitive proof of eligibility for weight loss surgery. When a patient comes to one of our seminars, with the hope of undergoing bariatric surgery, we will evaluate how their obesity or excess weight is affecting their lives – from limited mobility due to osteoarthritis to significant cardiac risks from high blood pressure and high cholesterol.

We suggest that patients use the BMI to track their weight loss progress and give themselves a benchmark for their goals. However, we do not want our patients to obsess over a number that is not necessarily accurate.